My son got himself an 1999 XJ this weekend. It was a friend of mines and she was moving and she gave it to him. I have worked on this XJ a few times. It has been sitting in the backyard for a year. i put in a new battery and added some fresh fuel and it started up and ran fine. We drove it 15 miles to home. i was watching the XJ and after a while i noticed it was running rich, black smoke coming out upon acceleration. My son did not notice any drive ability problems. I kind of expected the injectors would be gummed up. Well today we pulled the plugs and they were all black and sooty. So i am disregarding the injectors now since all plugs looked identical. The check engine light is not on. The air filter is a KN and is kind of cruddy, and that will need cleaning. The MAP sensor is suspect and the upstream O2 sensors seems to be an issue for people but i am still not throwing a code. It is the 4.0l Am I missing anything else to look for? I will eventually do a compression test, but the rig does run real good.